It is the objective of our research to produce pathophysiological information of practical importance which will lead to the increase in safety of diving and hyperbaric exposures and in the prevention and treatment of decompression sickness. We propose a three year program in the study of the major physiological factors of diving, on saturation decompressions, on the counter-perfusion/diffusion studies and the evaluation of the echocardiograph and acute respiratory crisis. A. Major Physiological Factors of Diving. The specific aim of this portion of the project is to clarify by means of venous gas embolism (VGE) detection, the role of four major physiological factors which may alter the incidence of decompression sickness. These factors are the response to submersion, cold exposure and exercise when submerged in cold water, and the effect of straining the musculo-skeletal system during decompression. B. Saturation Decompressions. The specific aims of this study are to test a technique of determining the fastest and safest speed of decompression from saturation exposures to nitrox and heliox mixtures. C. Counter-Perfusion/Diffusion Studies. The aim of this study is to determine if the brain can produce conter-perfusion/diffusion venous gas bubbles and if so, under what conditions. D. Evaluation of Echocardiography and Acute Respiratory Crisis (Chokes) Evaluate the echocardiography's ability to detect venous gas emboli.